<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    span, strong {
      float: left;
    }

    span {
      background-color: #f00;
    }

    strong {
      background-color: #0f0;
      margin-left: -10px;
    }
  </style>
</head>
<body>
  
  <span>我是span元素</span>
  <strong>我是strong元素</strong>

</body>
</html>